Intra‐MRI Head Motion Tracking and Correction: A Quantitative In Vivo Evaluation Framework

Prospective motion correction with data reacquisition based on fat navigators for T1-weighted brain MRI at 3T.

Impact of MRI slice thickness and fiducial marker orientation on geometric accuracy in multi‐echo GRE imaging for prostate radiotherapy planning

Abstract Background Precise target definition in prostate radiotherapy requires accurate computed tomography (CT)‐magnetic resonance imaging (MRI) image registration using gold fiducial markers (GFMs). While multi‐echo gradient recalled echo (ME GRE) sequences facilitate GFM identification, the quantitative impact of acquisition parameters on physical measurement accuracy remains insufficiently understood. Purpose This study evaluates how MRI slice thickness and marker orientation angle jointly affect GFM visualization and geometric accuracy to characterize the resulting localization uncertainties. Methods A kiwifruit‐based phantom (T1: 1603.3 ms; T2: 72.3 ms) that mimics the relaxation times of the human prostate was imaged with 3.0T MRI. Imaging was performed using a 3D ME GRE sequence with three slice thicknesses (1.0, 2.0, and 3.0 mm) and 12 orientation angles ranging from horizontal to 90°. Five multidisciplinary observers independently identified marker coordinates while blinded to the acquisition parameters. Subjective confidence scores were also recorded. Results Two‐way analysis of variance (ANOVA) revealed significant main effects for slice thickness (F(2, 144) = 32.03, p < 0.001) and orientation angle (F(11, 144) = 4.06, p < 0.001), with significant interaction between them (F (22, 144) = 2.72, p < 0.001). Mean measurement errors with 95% confidence intervals (CI) were 0.96 mm (95% CI: 0.70–1.22) for 1.0 mm, 1.49 mm (95% CI: 1.23–1.75) for 2.0 mm, and 2.00 mm (95% CI: 1.74–2.26) for 3.0 mm slices. The peak error reached 3.10 mm under the combination of a 3.0 mm slice and 15° orientation. Subjective confidence scores showed a significant negative correlation with physical measurement errors (r = −0.296, p < 0.001). Conclusions MRI slice thickness and marker orientation significantly impact GFM visualization accuracy. The results suggest that a 1.0 mm slice thickness offers a technical advantage for maintaining sub‐millimeter localization accuracy across various marker orientations and highly desirable for high‐precision radiotherapy planning.

Lesion-robust longitudinal brain CT registration via MR-guided image translation

Longitudinal brain computed tomography (CT) is routinely used to monitor disease progression in patients with focal lesions and other neuropathologies. Accurate registration across time points is essential for reliable quantitative analysis. However, this task remains challenging due to the intrinsically low soft-tissue contrast of CT, particularly between gray and white matter, and the presence of space-occupying lesions, which induce substantial anatomical deformation and violate the intensity-consistency assumptions underlying conventional registration methods. To address these challenges, we propose a lesion-robust framework for longitudinal brain CT registration based on MRguided image translation. Specifically, an Image-to-Image Schrödinger Bridge (I2SB) network is employed to translate CT images into pseudo-MR images with enhanced anatomical contrast. We then perform joint deformable registration on both pseudo-MR and original CT images, where pseudo-MR provides structurally informative guidance while CT enforces modality-consistent data fidelity. This joint formulation enables more reliable correspondence estimation in the presence of lesion-induced deformation and intensity inconsistencies. The resulting deformation field is subsequently applied to the original CT images to achieve accurate longitudinal alignment. We evaluate the proposed method on an in-house longitudinal CT dataset of patients with intracerebral hemorrhage. Experimental results demonstrate that our approach consistently outperforms conventional intensity-based registration methods as well as existing image-translation–assisted strategies in both quantitative metrics and visual alignment quality. By jointly leveraging contrast-enhanced structural cues and modality-consistent constraints, the proposed framework provides a robust solution for longitudinal brain CT registration in the presence of large lesions.

Comparison of accelerated MRI protocol approaches for clinical assessment of the knee.

Accelerated 2D DL, 3D Cube, and 3D qDESS protocols demonstrated diagnostic agreement and diagnostic image quality comparable to the conventional knee MRI protocol while reducing scan time to ~ 6 min.

Overcoming pitfalls in multi-stack diffusion MRI for tractography reconstruction of skeletal muscles

Accurate in vivo characterization of skeletal muscle structure is essential for understanding muscle function, assessing pathologies, and developing musculoskeletal models. Magnetic resonance imaging (MRI) and diffusion MRI enable visualization of muscle morphology and fibre architecture in vivo, but imaging skeletal muscles often requires an extended field of view. At large distances from the magnet isocentre, gradient non-linearities and magnetic field inhomogeneities can cause severe image distortions. Here, we present multi-stack structural and diffusion-tensor echo-planar images of the lower limb using selected stack lengths and acquisition parameters to provide realistic examples. Geometric distortions, fractional anisotropy maps, and tractography-reconstructed fibre tracts are used to demonstrate anatomical plausibility and consistency across overlapping slices. In the presented examples, pronounced distortions, compromised fat suppression, and fibre reconstruction errors are observed under off-isocentre imaging conditions. While shorter stack lengths may help reduce distortions, our examples also indicate that factors such as shimming strategy, participant positioning, and post-processing can influence image quality. Our work highlights key pitfalls in muscle diffusion MRI, providing practical guidance grounded in MRI physics to support the design of multi-stack MRI protocols. These considerations support more reliable multi-stack diffusion MRI for musculoskeletal research and biomechanical modelling.

AAPM Task Group 333 Report: Quality assurance for MRI‐guided focused ultrasound body systems

A quality assurance (QA) procedure for magnetic resonance‐guided focused ultrasound (MRgFUS) body systems was developed and tested at five institutions. The QA procedure is based on a custom‐designed phantom with tissue‐mimicking acoustic, MR, and thermal properties specific for MRgFUS. The data acquisition includes assessments of maximum temperature rise, targeting error, signal‐to‐noise ratio (SNR), and three‐dimensional thermal ablation spot size, which are to be tracked over longitudinal repetitions of the QA procedure. The procedure is appropriate for intermediate‐level QA, for example, every 20 patients or 6 months, and can be completed in approximately two hours. A subset of the full procedure is recommended for system verification either daily or before each patient (in addition to the vendor‐recommended procedure). The phantom and QA procedure have been tested on a variety of custom and commercially available MRgFUS body systems, including systems with 1.5 and 3.0 T static magnetic fields. Normal variability in measurements based on data from five functional MRgFUS body systems over periods of at least 6 months is reported and establishes quantitative criteria for passing the QA test. This QA procedure may be used to increase confidence in the safety and performance of MRgFUS treatments.